The present invention relates to a terminal system, mainly provided in electric wiring instruments used in home, which is used to connect a cable when the above instruments such as a plug, a plug receptacle, ceilings and a switch, are newly provided, and added or replaced. The present terminal system does not require screws for attachment, therefore, a man with no expert knowledge of electricity can easily and safely connect the above described instrument with the cable, by simply inserting the cable into the hole without a tool.
Prior Art
With regard to the terminal system which connects the cable by this kind of easy means, many inventions have been proposed, and some of them are sent to markets, and it is almost common basic principle that a spring is provided in the above described terminal system in order to connect and fix the cable by pressure.
The terminal system shown in FIG. 9 is a conventional example. In this system, a plate having superiority in spring force and in conductivity, such as phosphor bronze and brass, is used. The retaining portions 10A and 10B of the connector 10 are formed by pressure so that a gap may exist at the side to which the cable 30 is inserted at one side and the two plates may closely contact at the other side. When the cable 30 is inserted from the shown side of the above described retaining portions 10A and 10B, namely, from the gap side, the cable can be inserted against relatively small mechanical resistance. When the cable is pulled, due to the interaction of the spring force induced by said retaining portions 10A and 10B and the shapes of said retaining portions 10A and 10B, a large resistance against the pulling load is induced, and this ensures the connection of the above cable 30. The difference of the mechanical resistance between inserting and pulling as shown in FIG. 10, is generated from the interaction of the angle .beta., between the retaining portions 10A, 10B and the cable 30, and the spring force from the above retaining portions 10A and 10B, pressing the cable 30. In the range of angle being less than 45.degree., the relationship between the angle .beta. and the mechanical resistance difference between inserting and pulling, is proportional. In the extreme case, when the angle .beta. is zero, in other words, both of said retaining portions 10A and 10B are formed in parallel with the cable 30, this means that the resistance difference between inserting and pulling becomes zero. In this case, inserting and pulling the cable 30 can be done with same force. The above explanation, at the same time, means the following relationship. Namely, when the contact area, between said cable 30 and said retaining portions 10A and 10B, is increased so as to send the large current, the above angle .beta. becomes zero and the function to retain the cable 30 is decreased, on the contrary, when the angle .beta. is increased to enhance the function to retain the cable 30, the above described contact area becomes a point, and the allowable current is reduced.
Through the above reasons, this kind of conventional terminal system, in order to endure the load of pulling cable considered to be induced in usual use, necessarily requires the angle, between the cable 30 and the above retaining portions 10A and 10B, to be more than fixed value, therefore, the above contact area becomes small. As a result, it can be said that this kind of conventional terminal system is not suitable to large current cable connection.
The problem explained above is the common problem in the conventional terminal systems employing spring force to connect the cable. Various kinds of terminal systems, except the above example have been proposed, however, there is no invention which essentially solved this problem.